Video comparison using color histograms

ABSTRACT

Methods, apparatus and articles of manufacture for video comparison using color histograms are disclosed. Example methods disclosed herein to compare video sequences include determining a color histogram corresponding to an input video sequence based on color values of pixels sampled from a plurality of video frames of the input video sequence. Such example methods also include adjusting the color histogram corresponding to the input video sequence based on a first reference color histogram corresponding to a first reference video sequence to determine a first adjusted color histogram corresponding to the input video sequence. Such example methods further include comparing the adjusted color histogram and the first reference color histogram to determine whether the first reference video sequence matches the input video sequence.

This patent arises from a continuation of U.S. patent application Ser.No. 13/324,692 (now U.S. Pat. No. 8,897,554), which is entitled “VIDEOCOMPARISON USING COLOR HISTOGRAMS” and which was filed on Dec. 13, 2011.U.S. patent application Ser. No. 13/324,692 is hereby incorporated byreference in its entirety.

FIELD OF THE DISCLOSURE

This disclosure relates generally to comparing videos and, moreparticularly, to video comparison using color histograms.

BACKGROUND

Image processing techniques for comparing videos can have many practicalapplications. For example, video comparison techniques that compare aninput, or test, video to one or more reference videos can be applied tothe detection and identification of broadcast, on-demand and/or onlinemedia content selected for viewing by viewers, the detection andverification of advertisements presented with or otherwise accompanyingbroadcast, on-demand and/or online media content, the detection andverification of product placements in television programming, etc. Priorvideo comparison techniques include techniques that compare differentvideos using video and/or image signatures and techniques that performpixel-by-pixel comparison of video frames from the different videos.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example video comparison system forcomparing videos using color histograms as disclosed herein.

FIG. 2 is a block diagram of an example video frame sampler for samplinga sequence of video frames of a video in the example video comparisonsystem of FIG. 1.

FIGS. 3A-3B illustrate example video frame sampling operations that maybe performed by the example video frame sampler of FIG. 2.

FIG. 4 is a block diagram of an example histogram generator forgenerating color histograms in the example video comparison system ofFIG. 1.

FIG. 5 is a block diagram of an example histogram comparator forcomparing color histograms in the example video comparison system ofFIG. 1.

FIG. 6 is a block diagram of an example bin adjuster that may be used toimplement the example histogram comparator of FIG. 5.

FIG. 7 is a block diagram of an example comparison metric determinerthat may be used to implement the example histogram comparator of FIG.5.

FIG. 8 is a flowchart representative of example machine readableinstructions that may be executed to implement the example videocomparison system of FIG. 1.

FIG. 9 is a flowchart representative of example machine readableinstructions that may be executed to implement the example histogramgenerator of FIG. 4, and/or used to implement portions of the examplemachine readable instructions of FIG. 8.

FIG. 10 is a flowchart representative of example machine readableinstructions that may be executed to implement the example bin adjusterof FIG. 6 in the example histogram comparator of FIG. 5, and/or used toimplement portions of the example machine readable instructions of FIG.8.

FIG. 11 is a flowchart representative of example machine readableinstructions that may be executed to implement the example comparisonmetric determiner of FIG. 7 in the example histogram comparator of FIG.5, and/or used to implement portions of the example machine readableinstructions of FIG. 8.

FIG. 12 is a flowchart representative of example machine readableinstructions that may be executed to process a set of reference videosto determine a respective set of reference color histograms for use bythe example video comparison system of FIG. 1.

FIG. 13 is a block diagram of an example processing system that mayexecute the example machine readable instructions of FIGS. 8-11 and/or12 to implement the example video comparison system of FIG. 1, theexample video frame sampler of FIG. 2, the example histogram generatorof FIG. 4, the example histogram comparator of FIG. 5, the example binadjuster of FIG. 6 and/or the example comparison metric determiner ofFIG. 7.

DETAILED DESCRIPTION

Methods, apparatus and articles of manufacture for video comparisonusing color histograms are disclosed herein. In general, a colorhistogram for a video (e.g., corresponding to a video frame or asequence of video frames from a video) includes a set of bins (alsoreferred to herein as color bins) representing a respective set ofpossible colors that may be included in the video frame(s). For example,a particular bin corresponding to a particular color (or, in otherwords, a particular color bin) can have a bin value representing a countof the number of pixels of the video frame(s) (or a sampledversion/subset of the video frame(s)) having that particular color. Insome examples, the color histogram for a video can be stored in a dataformat that may be used as a signature (e.g., a unique or substantiallyunique proxy) representative of the video. In such examples, the colorhistogram for a video may be referred to as the video's color histogramsignature.

An example method disclosed herein to compare a first video and a secondvideo using color histograms includes obtaining a first color histogramcorresponding to a sequence of frames of the first video (e.g., areference video), and obtaining a second color histogram correspondingto a sequence of frames of the second video (e.g., a test video, alsoreferred to herein as an input video). The disclosed example method alsoincludes determining a first comparison metric based on differencesbetween bin values of the first color histogram and adjusted bin valuesof the second color histogram. The disclosed example method furtherincludes determining whether the first video and the second video matchbased on the first comparison metric.

As described in detail below, in some examples, the method obtains acolor histogram corresponding to a sequence of frames of a video bysampling the sequence of video frames from the video and furthersampling a set of all or at least some of the pixels from each one ofthe sequence of video frames (e.g., using uniform or random sampling ofpixels in each of the video frames). The example method then quantizescolor values of the set of pixels from the sequence of video frames andincludes the set of pixels in color bins of the color histogram based onthe quantized color values of the set of pixels.

In some examples, the disclosed example method determines the adjustedbin values of the second color histogram (for use in determining thefirst comparison metric) by scaling bin values of the second colorhistogram by a scale factor (e.g., such as a scale factor of 2 oranother value) to determine scaled bin values of the second colorhistogram. The example method then determines an adjusted bin value ofthe second color histogram for a particular color bin to be a smaller(e.g., minimum) of a scaled bin value of the second color histogram forthe particular color bin or a respective bin value of the first colorhistogram for the particular color bin. In some examples, the methoddetermines the first comparison metric by determining the differencesbetween the bin values of the first color histogram and the respectiveadjusted bin values of the second color histogram, and summing thedifferences to determine the first comparison metric.

In some examples, the disclosed example method determines that the firstvideo and the second video match, or substantially match, when the firstcomparison metric is less than or equal to a threshold. In someexamples, the method further includes determining a second comparisonmetric based on differences between bin values of the second colorhistogram and adjusted bin values of the first color histogram. In suchexamples, the method determines whether the first video and the secondvideo match based on the first comparison metric and the secondcomparison metric. For example, the method can determine that the firstvideo and the second video match when at least one of the firstcomparison metric or the second comparison metric is less than or equalto the threshold. The example method can also determine that the firstvideo and the second video match do not match when the first comparisonmetric and the second comparison metric are each greater than thethreshold.

As noted above, image processing techniques for comparing videos canhave many practical applications. However, at least some prior videocomparison techniques are limited in that they are able to indicate thattwo videos match only when the videos are identical or nearly identical.However, in at least some circumstances, it may be beneficial toidentify video content as belonging to a group of similar, but notidentical, content. Groups of similar video content include, forexample: (1) groups of commercial advertisements having the same videobut different audio tracks; (2) groups of commercial advertisementshaving minor producer modifications, such as one scene being replacedwith a different scene in an otherwise similar advertisement; (3) groupsof commercial advertisements in which different text is overlaid on athe same video content; (4) groups of video clips corresponding to thesame content but with different network logos overlaid on differentvideo clips; (5) groups of video clips corresponding to the same contentbut truncated to different lengths; (6) groups of video clipscorresponding to the same content but having different image/framesizes; etc. Unlike such prior video comparison techniques, videocomparison using color histograms as disclosed herein can identifyvideos that are identical (or nearly) identical, and can also identifyvideos that have similar, but not necessarily identical, content.

Turning to the figures, a block diagram of an example video comparisonsystem 100 that may be used to compare videos using color histograms inaccordance with the example methods, apparatus and articles ofmanufacture disclosed herein is illustrated in FIG. 1. The videocomparison system 100 includes an example reference video library 105that stores a set of one or more reference videos for comparison with atest video, also referred to herein as an input video. The referencevideo(s) stored in the reference video library 105 can correspond to anytype(s) of video(s) obtained from any type(s) of source(s). For example,the reference videos stored in the reference video library 105 caninclude videos of broadcast, on-demand and/or online media contactcapable of being selected for viewing by viewers, videos ofadvertisements captured from broadcast, on-demand and/or online mediacontent, videos of product placements observed in televisionprogramming, etc. The reference video library 105 can correspond to anytype or combination of temporary and/or permanent tangible storagemedia, such as one or more of cache, volatile memory, flash memory, diskstorage, etc., including but not limited to one or more of the massstorage devices 1330 and/or volatile memory 1318 in the exampleprocessing system 1300 of FIG. 13, which is described in greater detailbelow.

The example video comparison system 100 also includes an example videoframe sampler 110 to sample or otherwise obtain a respective sequence ofvideo frames from a respective reference video stored in the referencevideo library 105. The video frame sampler 110 samples a particularreference video at a frame rate, resolution and duration to obtain thesequence of video frames for the reference video. In some examples, theframe rate, resolution and/or duration that determine how the videoframe sampler 110 is to sample reference video(s) can be specified asvariable input parameters to the video comparison system 100 (e.g., totrade-off accuracy vs. processing speed). Additionally or alternatively,one or more of these parameters can be configuration parameter(s) setduring initialization of the video comparison system 100.

In some examples, the video comparison system 100 of FIG. 1 includes anexample composite reference image storage 115 to store a compositereference image formed by combining the sequence of video frames (alsoreferred to herein as the sequence of reference video frames) obtainedby the video frame sampler 110 for a particular reference video. Forexample, the video frame sampler 110 can tile reference video frames inthe sequence of video frames for a particular reference video to form atiled array of reference video frames representing the reference video.This tiled array of reference video frames is stored in the compositereference image storage 115 as the respective composite reference imagefor this particular reference video. The horizontal and verticaldimensions (e.g., in numbers of frames) for the tiled image arraysforming the composite reference images stored in the composite referenceimage storage 115 can be specified as variable input parameters to thevideo comparison system 100 and/or can be configuration parameter(s) setduring initialization of the video comparison system 100.

In some examples, the video frame sampler 110 may sample a subset of thereference video frames from the sequence of reference video frames toform a composite reference image representing the reference video. Insuch examples, the video frame sampler 110 may obtain reference videoframes at a video frame rate (e.g., 30 frames per second or some otherframe rate) and then sample a subset of these reference video frames atsampled frame times (t) corresponding to a subset of the frame times(e.g., time boundaries corresponding to a 1/30 second sampling intervalor some other frame sampling interval) at which the reference videoframes are obtained. For example, the video frame sampler 110 can sample(e.g., select) reference video frames at sampled frame times that areselected randomly from the set of frame times at which the referencevideo frames exist (also referred to herein as random sampling), and/orthat are selected uniformly from the set of frame times at which thereference video frames exist (also referred to herein as uniformsampling), etc. Additionally or alternatively, in some examples, thevideo frame sampler 110 may include sampled pixel(s) and/or subregion(s)of a particular reference video frame, rather than the entire referencevideo frame, in the reference composite image. For example, the videoframe sampler 110 may select pixel(s) (and/or subregion(s) of referencevideo frames having specified or otherwise determined shape(s) andsize(s) (e.g., rectangular)) at specified or otherwise determinedhorizontal (x) and vertical (y) integer pixel coordinates(s), and atsampled frame times (t) selected (e.g., randomly or uniformly) from theset of valid reference video frame times (e.g., 1/30 second timeintervals), for inclusion in a sequence or array of reference videoframes forming the composite reference image representing the referencevideo. The composite reference image storage 115 can correspond to anytype or combination of temporary and/or permanent tangible storagemedia, such as one or more of cache, volatile memory, flash memory, diskstorage, etc., including but not limited to one or more of the massstorage devices 1330 and/or volatile memory 1318 in the exampleprocessing system 1300 of FIG. 13, which is described in greater detailbelow.

The video comparison system 100 of the illustrated example includes anexample histogram generator 120 to generate a respective reference colorhistogram for each reference video included in the set of referencevideos stored in the reference video library 105. The resulting set ofone or more reference color histograms generated by the histogramgenerator 120 are stored in an example reference histogram library 125included in the video comparison system 100. For example, a referencecolor histogram generated by the histogram generator 120 for aparticular reference video includes a set of bins (also referred toherein as color bins) representing a respective set of possible colorsthat may be included in the sequence of video frames obtained by thevideo frame sampler 110 for the reference video. For a particular bincorresponding to a particular color (or, in other words, a particularcolor bin), the histogram generator 120 determines a bin value for thecolor bin that represents a count of the number of pixels of thereference video frames included in the sequence of video frames for theparticular reference video (or a sampled version/subset of the sequenceof reference video frames) having the particular color associated withthe color bin. In some examples, the histogram generator 120 processesreference video frames (and/or sampled pixels(s)/subregion(s) of thereference video frames) individually (e.g., sequentially as the framesand/or sampled pixels(s)/subregion(s) are obtained and/or buffered bythe video frame sampler 110) to count pixel colors and update thereference color histogram for a particular reference video beingprocessed. In such examples, the composite reference image storage 115and any composite image processing by the video frame sampler 110 can beomitted from the video comparison system 100. In other examples (e.g.,in which the composite reference image storage 115 is present), thehistogram generator 120 processes the respective composite referenceimage determined for the particular reference video to determine therespective reference color histogram for the reference video. Thereference histogram library 125 used to store the set of reference colorhistograms generated by the histogram generator 120 can correspond toany type or combination of temporary and/or permanent tangible storagemedia, such as one or more of cache, volatile memory, flash memory, diskstorage, etc., including but not limited to one or more of the massstorage devices 1330 and/or volatile memory 1318 in the exampleprocessing system 1300 of FIG. 13, which is described in greater detailbelow.

In the example of FIG. 1, the video comparison system 100 uses the setof reference histograms stored in the reference histogram library 125 tocompare a reference video stored in the reference video library 105 witha test video (also referred to herein as an input video) obtained via anexample test video interface 130. For example, the video comparisonsystem 100 determines whether the test video obtained via the test videointerface 130 matches a selected reference video stored in the referencevideo library 105 and, if so, identifies that the matching referencevideo is the same as or is at least similar to the test video. The testvideo interface 130 can be implemented by, for example, a camera orother image sensing device to capture a video of a display of amultimedia presentation device (e.g., a television, computer monitor,smartphone, etc.) in the viewing field of the camera/imaging device,etc. Additionally or alternatively, the test video interface 130 can beconfigured to electrically, optically or otherwise communicativelycouple with a video output of the multimedia presentation device.Additionally or alternatively, the test video interface 130 can beimplemented by a computer or other processing device configured toobtain test videos from one or more network sources (e.g., servers)communicatively coupled to the test video interface 130 (e.g., via theInternet and/or one or more other networks).

The example video comparison system 100 also includes an example videoframe sampler 135 to sample or otherwise obtain a respective sequence ofvideo frames from the test video obtained via the test video interface130. Like the video frame sampler 110, the video frame sampler 135samples the test video at a frame rate, resolution and duration toobtain the sequence of video frames for the test video. In someexamples, the frame rate, resolution and/or duration that determine howthe video frame sampler 135 is to sample the test video can be specifiedas variable input parameters to the video comparison system 100 (e.g.,to trade-off accuracy vs. processing speed). Additionally oralternatively, one or more of these parameters can be configurationparameter(s) set during initialization of the video comparison system100. The frame rate, resolution and/or duration of the sequence of videoframes obtained by the video frame sampler 135 for the test video can bethe same as or different from the frame rate, resolution and/or durationof the sequence of video frames obtained by the video frame sampler 110for a reference video to be compared with the test video. In someexamples, the video frame samplers 110 and 135 may be implemented by thesame video frame sampler, whereas in other examples, the video framesamplers 110 and 135 may be implemented by different video framesamplers. An example implementation of the video frame samplers 110 and135 is illustrated in FIG. 2, which is described in greater detailbelow.

In some examples, the video comparison system 100 of FIG. 1 includes anexample composite test image storage 140 to store a composite test imageformed by combining the sequence of video frames (also referred toherein as the sequence of test video frames) obtained by the video framesampler 135 for the test (e.g., input) video. For example, the videoframe sampler 135 can tile test video frames in the sequence of videoframes of the test video to form a tiled array of test video framesrepresenting the test video. This tiled array of test video frames isstored in the composite test image storage 140 as the respectivecomposite test image for this particular test (e.g., input) video. Thehorizontal and vertical dimensions (e.g., in numbers of frames) for thetiled image array forming the composite test image stored in thecomposite test image storage 140 can be specified as variable inputparameters to the video comparison system 100 and/or can beconfiguration parameter(s) set during initialization of the videocomparison system 100. Furthermore, the horizontal and verticaldimensions for the composite test image stored in the composite testimage storage 140 can be the same as or different from the horizontaland vertical dimensions for the composite reference image(s) stored inthe composite reference image storage 115.

In some examples, the video frame sampler 135 may sample a subset of thetest video frames from the sequence of test video frames to form acomposite test image representing the test video. In such examples, thevideo frame sampler 135 may obtain test video frames at a video framerate (e.g., 30 frames per second or some other frame rate) and thensample a subset of these test video frames at sampled frame times (t)corresponding to a subset of the frame times (e.g., time boundariescorresponding to a 1/30 second sampling interval or some other framesampling interval) at which the test video frames are obtained. Forexample, the video frame sampler 135 can sample (e.g., select) testvideo frames at sampled frame times that are selected randomly from theset of frame times at which the test video frames exist (also referredto herein as random sampling times), and/or that are selected uniformlyfrom the set of frame times at which the test video frames exist (alsoreferred to herein as uniform sampling times), etc. Additionally oralternatively, in some examples, the video frame sampler 135 may includesampled pixel(s) and/or subregion(s) of a particular test video frame,rather than the entire test video frame, in the test composite image.For example, the video frame sampler 135 may select pixel(s) (and/orsubregion(s) of test video frames having specified or otherwisedetermined shape(s) and size(s) (e.g., rectangular)) at specified orotherwise determined horizontal (x) and vertical (y) integer pixelcoordinates (s), and at sampled frame times (t) selected (e.g., randomlyor uniformly) from the set of valid test video frame times (e.g., 1/30second time intervals), for inclusion in a sequence or array of testvideo frames forming the composite test image representing the testvideo. The composite test image storage 140 can correspond to any typeor combination of temporary and/or permanent tangible storage media,such as one or more of cache, volatile memory, flash memory, diskstorage, etc., including but not limited to one or more of the massstorage devices 1330 and/or volatile memory 1318 in the exampleprocessing system 1300 of FIG. 13, which is described in greater detailbelow. Furthermore, the reference video library 105, the compositereference image storage 115, the reference histogram library 125 and thecomposite test image storage 140 can be implemented by the same ordifferent storage media.

The video comparison system 100 of the illustrated example includes anexample histogram generator 145 to generate a color histogram for thetest video obtained from the test video interface 130. As such, thecolor histogram generated by the histogram generator 145 for the testvideo is also referred to herein as the test color histogram. Similar tothe reference color histogram(s) generated by the histogram generator120, a test color histogram generated by the histogram generator 145 forthe test video includes a set of bins (e.g., color bins) representing arespective set of possible colors that may be included in the sequenceof video frames obtained by the video frame sampler 135 for the testvideo. For a particular bin corresponding to a particular color (e.g.,for a particular color bin), the histogram generator 145 determines abin value for the color bin that represents a count of the number ofpixels of the test video frames included in the sequence of video framesfor the test video (or a sampled version/subset of the sequence of testvideo frames) having the particular color associated with the color bin.In some examples, the histogram generator 145 processes test videoframes (and/or sampled pixels(s)/subregion(s) of the test video frames)individually (e.g., sequentially as the frames and/or sampledpixels(s)/subregion(s) are obtained and/or buffered by the video framesampler 135) to count pixel colors and update the test color histogramfor the test video being processed. In such examples, the composite testimage storage 140 and any composite image processing by the video framesampler 135 can be omitted from the video comparison system 100. Inother examples (e.g., in which the composite test image storage 140 ispresent), the histogram generator 145 processes the respective compositetest image determined for the test image to determine the test colorhistogram for the test video. In some examples, the histogram generators120 and 145 may be implemented by the same histogram generator, whereasin other examples, the histogram generators 120 and 145 may beimplemented by different histogram generators. An example implementationof the histogram generators 120 and 145 is illustrated in FIG. 4, whichis described in greater detail below.

The example video comparison system 100 of FIG. 1 includes an examplehistogram comparator 150 to compare the test color histogram generatedby the histogram generator 145 for the test video with a reference colorhistogram stored in the reference histogram library 125 for a particular(e.g., selected) reference video to be compared with the test video. Insome examples, the histogram comparator 150 determines one or morecomparison metrics that quantify the results of comparing a particularreference video with the test video. For example, the histogramcomparator 150 determines a first comparison metric quantifyingcomparison of a particular reference video with the test video based ondifferences between bin values of the reference color histogram for theparticular reference video and adjusted bin values of the test colorhistogram. As described in greater detail below, the histogramcomparator 150 determines adjusted bin values of the test colorhistogram based on comparing scaled bin values of the test colorhistogram with the bin values of the reference color histogram for theparticular reference video. Because the adjusted bin values aredetermined based on the bin values of the particular reference colorhistogram, the histogram comparator 150 may determine different testhistogram adjusted bin values when comparing the test video to differentreference videos.

In some examples, the histogram comparator 150 determines a secondcomparison metric quantifying comparison of the particular referencevideo with the test video by swapping the roles of the reference colorhistogram and the test color histogram in determining the comparisonmetric. In other words, in such an example, the histogram comparator 150determines the second comparison metric based on differences between binvalues of the test color histogram and adjusted bin values of thereference color histogram for the particular reference video beingcompared with the test video. For example, similar to determining theadjusted bin values of the test color histogram, the histogramcomparator 150 determines adjusted bin values of the reference colorhistogram for the particular reference video based on comparing scaledbin values of the reference color histogram with the bin values of thetest color histogram.

Adjustment of test color histogram bin values (and reference colorhistogram bin values, in some examples), as described in greater detailbelow, can permit the video comparison system 100 to identify matchingvideos (e.g., videos that are identical or at least having similarcontent) even when the color histograms for the videos are different if,for example, the respective bin values of the two color histograms forthe color bins are within a scale factor of each other. Such adjustmentof the bin values of the test and/or reference color histograms canenable the video comparison system 100 to identify groups of similar,but not identical, video content, such as: (1) groups of commercialadvertisements having the same video but different audio tracks; (2)groups of commercial advertisements having minor producer modifications,such as one scene being replaced with a different scene in an otherwisesimilar advertisement; (3) groups of commercial advertisements in whichdifferent text is overlaid on the same video content; (4) groups ofvideo clips corresponding to the same content but with different networklogos overlaid different video clips; (5) groups of video clipscorresponding to the same content but truncated to different lengths;(6) groups of video clips corresponding to the same content but havingdifferent image/frame sizes; etc. In some examples, the scale factor isused to determine the scaled bin values of a particular color histogram(from which the adjusted bin values are determined). In such examples,the scale factor can be specified as a variable input parameter to thevideo comparison system 100 (e.g., to trade-off false matching vs.missed matching results during system operation). Additionally oralternatively, the scale factor can be a configuration parameter that isset during initialization of the video comparison system 100.

The histogram comparator 150 of the illustrated example also processesthe one or more comparison metrics to determine whether the test videoobtained via the test video interface 130 matches the particularreference video selected from the reference video library 105. Forexample, the histogram comparator 150 may determine that the test videomatches the particular reference video stored in the reference videolibrary 105 if at least one of the comparison metrics quantifyingcomparison of the reference video with the test video is less than orequal to a threshold. In some examples, the threshold can be specifiedas a variable input parameter to the video comparison system 100 (e.g.,to trade-off false matching vs. missed matching results during systemoperation). Additionally or alternatively, the threshold can be aconfiguration parameter that is set during initialization of the videocomparison system 100.

In the illustrated example of FIG. 1, the video comparison system 100further includes an example results interface 155 to provide the resultsof comparing the test video obtained via the test video interface 130 toa particular reference video selected from the reference video library105. For example, the results interface 155 reports or otherwise outputsthe video comparison results using any appropriate data format forpresentation to a user and/or sending to a receiving device. Forexample, the results interface 155 indicates whether the test video hasbeen determined to match a selected reference video stored in thereference video library 105. In some examples, the results interface 155also reports the comparison metric(s) associated with the matchingreference video.

A block diagram of an example video frame sampler 200 that may be usedto implement either or both of the video frame samplers 110 and/or 135of FIG. 1 is illustrated in FIG. 2. The video frame sampler 200 of theillustrated example includes an example image sampler 205 to capture orotherwise sample a sequence of video frames from a video input to thevideo frame sampler 200 (e.g., such as a reference video or a test videoas described above). In the illustrated example, the image sampler 205samples the input video at a frame rate, resolution and duration thatare configured by an example sampling controller 210. In some examples,the sampling frame rate, resolution and duration parameters may bevariable input parameters and/or initial configuration parameters (or acombination thereof) provided to sampling controller 210. For example,the sampling controller 210 can be configured with sampling frame rate,resolution and duration parameters to cause the image sampler 205 tosample an input image at a frame rate of one frame every ⅕=0.2 seconds(or some other rate), with a frame resolution of 128×128 pixels (or someother resolution) and a duration of 30 seconds (or some other duration).

Example video frame sampling operations that may be performed by theexample video frame sampler 200 of FIG. 2 are illustrated in FIGS. 3A-B.In particular, FIG. 3A illustrates example composite images 305 and 310that may be formed by the video frame sampler 200 for differentrespective input videos. The composite images 305 and 310 may beprocessed by, for example, the histogram generators 120 and/or 145 togenerate color histograms for the input videos represented by thecomposite images 305 and 310, as described above. For example, thecomposite image 305 may be a composite reference image corresponding toa reference video sampled by the video frame sampler 200 implementingthe video frame sampler 110 of FIG. 1, and the composite image 310 maybe a composite test image corresponding to a test video sampled by thevideo frame sampler 200 implementing the video frame sampler 135 ofFIG. 1. In the illustrated example composite image 305, the video framesampler 200 tiles the reference video frames in the sequence of videoframes sampled from the reference video into a tiled array containingrows of four (4) reference video frames, with the number of rowsdetermined by the duration and sampling rate used to sample thereference video. In the illustrated example composite image 310, thevideo frame sampler 200 tiles the test video frames in the sequence ofvideo frames sampled from the test video into a tiled array containingrows of four (4) test video frames, with the number of rows determinedby the duration and sampling rate used to sample the test video.

As illustrated in the examples of FIG. 3A, the sizes of the compositeimages determined for different videos may be different based on, forexample, different frame rate, resolution and duration parameters usedto configure the sampling of different videos. In examples in which thevideo frame sampler 200 forms composite images for sampled videos, suchas the composite images 305 and/or 310, the composite image for aparticular video can be processed, as described above and in furtherdetail below, to determine a color histogram for the particular video.In other examples, the video frame sampler 200 may not form a compositeimage for a particular video and, instead, the color histogram for theparticular video is formed by processing the sequence of video framessampled from the video (and/or sampled pixels(s)/subregion(s) of thevideo frames) individually and accumulating the bin counts for thedifferent video frames to form the color histogram for the particularvideo.

FIG. 3B illustrates an example operation 350 of the video frame sampler200 of FIG. 2 in which the video frame sampler 200 samples pixel(s)(and/or subregion(s)) of video frames of a video (possibly afterbuffering) to form the sequence of pixels (or the composite image) fromwhich the color histogram representative of the video is to bedetermined. As illustrated in the example of FIG. 3B, the video framesampler 200 samples (e.g., selects) pixel(s) (and/or subregion(s)) athorizontal (x) and vertical (y) integer pixel coordinates(s), and atsampled frame times (t) selected (e.g., randomly or uniformly) from theset of valid frame times (e.g., 1/30 second time intervals) for thevideo frames of the video. For example, in the operation 350, the videoframe sampler 200 selects video frames 351-355 at sampled frame timest1-t5, respectively. For frame 351 having sampled time t1, the videoframe sampler 200 samples (e.g., selects) pixels (or regions) at pixelcoordinates (x1 a, y1 a) and (x1 b, y1 b). Similarly, the video framesampler 200 samples pixels (or regions) at pixel coordinates (x2 a, y2a) and (x2 b, y2 b) for frame 352 having sampled time t2, samples pixels(or regions) at pixel coordinates (x3 a, y3 a) and (x3 b, y3 b) forframe 353 having sampled time t3, samples pixels (or regions) at pixelcoordinates (x4 a, y4 a) and (x4 b, y4 b) for frame 354 having sampledtime t4, and samples pixels (or regions) at pixel coordinates (x5 a, y5a) and (x5 b, y5 b) for frame 355 having sampled time t5. The pixels (orregions) at pixel coordinates (x1 a, y1 a), (x1 b, y1 b), (x2 a, y2 a),(x2 b, y2 b), (x3 a, y3 a), (x3 b, y3 b), (x4 a, y4 a), (x4 b, y4 b),(x5 a, y5 a) and (x5 b, y5 b) are then included in the sequence ofpixels (or composite image) from which the color histogramrepresentative of the video is to be determined. Although the samenumber of pixels (or regions) are sampled from each of the sampled videoframes in the illustrated example operation 350, in other exampleimplementations, the video frame sampler 200 can sample differentnumbers of pixels (or regions) from different video frames of the videofor which a color histogram is to be determined.

A block diagram of an example histogram generator 400 that may be usedto implement either or both of the histogram generators 120 and/or 145of FIG. 1 is illustrated in FIG. 4. The histogram generator 400 of theillustrated example includes an example image sampler 405 to sample aninput image to determine a set of pixels of the image. The input imagesamples by the image sampler 405 can correspond to a composite image(e.g., such as a composite reference image or a composite test image, asdescribed above) or a video frame sampled from a video (e.g., such as areference video frame sampled from a reference video or a test videoframe sampled from a test video). For example, the image sampler 405 cansample a subset or all of the pixels of the input image to obtain theset of pixels from which the color histogram is to be determined for thevideo from which the input image was obtained. In some examples, theimage sampler 405 employs uniform sampling to sample a number of pixels(e.g., such as 1000 or some other number) that are uniformly-spaced inthe input image (e.g., and that form a uniformly spaced grid of pixelsin the image) to obtain the sampled set of pixels of the image. In otherexamples, the image sampler 405 employs random sampling to randomlysample a number of pixels (e.g., such as 1000 or some other number) inthe input image to obtain the sampled set of pixels of the image. Insome examples, the image sampler 405 can be omitted and all of thepixels of the image are included in the set of pixels processed by thehistogram generator 400 to determine the color histogram for the videocorresponding to the input image.

The histogram generator 400 of FIG. 4 also includes an example colorquantizer 410 to quantize the color values of the pixels in the set ofpixels of the input image. Each pixel of the image is associated with aset of color values, such as three color values corresponding to a redcolor value, a green color value and a blue color value. In theillustrated example, the color quantizer 410 quantizes each color valueof a pixel into a set of levels. For example, the color quantizer 410may use any appropriate quantization technique to quantize the red colorvalue of each pixel into R intensity levels, the green color value ofeach pixel into G intensity levels, and the blue color value of eachpixel into B intensity levels. The values of R, G and B can be the sameor different, and may be variable input parameters and/or initialconfiguration parameters of the histogram generator 400.

The number of levels into which the color quantizer 410 quantizes eachcolor value determines the resulting number of possible colorcombinations that can be represented by the quantized pixels, whichcorresponds to the number of color bins of the color histogramdetermined by the histogram generator 400. In other words, theaforementioned quantization of the red, green and blue color valuesyields R×G×B color combinations and, thus, the color histogramdetermined by the histogram generator 400 of the illustrated example hasR×G×B color bins. For example, if R=G=B=8, then the total number ofpossible color combinations and, thus, the total number of color bins is8×8×8=512. Color quantization as performed by the color quantizer 410can reduce processing requirements and improve video matchingrobustness, such as in circumstances in which small color variationsbetween videos occur due to, for example, video frame smoothing and/orother processing of the test and/or reference videos.

In other examples, the quantized color values of a particular pixel arecombined (e.g., concatenated) with the quantized color values of one ormore other pixels in a neighborhood of the particular pixel to determinethe quantized color combination for the particular pixel. The value ofthe quantized color combination for the particular pixel (e.g., thevalue obtained by combining the quantized color values of the particularpixel with those of the neighboring pixel(s)) then determines thehistogram color bin in which the pixel is to be included. Like before,the resulting number of possible color combinations that can berepresented by the combination of quantized pixels in a neighborhoodcorresponds to the number of color bins of the color histogramdetermined by the histogram generator 300. In other words, if thequantized color values of a particular pixel are combined with thequantized color values of N-1 neighboring pixels, then the number ofpossible color combinations associated with combining the neighboringquantized pixels and, thus, the number if color histogram bins is(R×G×B)^(N). For example, if R=G=B=2 (corresponding to binary, or 1 bit,quantization) and the quantized color values of a particular pixel arecombined with the quantized color values of a first neighbor pixellocated a first number (e.g., 5 or some other number) of pixels up fromthe particular pixel and a second neighbor pixel located a second number(e.g., 5 or some other number) of pixels to the left of the particularpixel, then the total number of possible color combinations for thecombination of a pixel with its N-1 neighboring pixels and, thus, thetotal number of color bins is (2×2×2)³=512.

In the illustrated example, the histogram generator 400 includes anexample color counter 415 to count the numbers of times each possiblequantized color combination appears in the sampled set of pixels of theinput image. For example, the color counter 415 can store each possiblecolor combination that can be exhibited by the quantized pixels as arespective element of a data array (e.g., with the integer value of aparticular color combination forming the index for its respectiveelement in the data array). In such an example, the color counter 415increments the values of the array elements to count the numbers oftimes each different color combination appears in the quantized set ofpixels. To determine a color histogram corresponding to a particularvideo, the color counter 415 further increments the values of the arrayelements to count the numbers of times each different color combinationappears in the respective, quantized sets of pixels for the input framesforming the sequence of input frames sampled from the particular videoand applied to the histogram generator 400 for processing. The resultingcounts of the different color combinations appearing in the quantizedsets of pixels of the sequence of input images forms the color histogramof the video corresponding to this sequence of input images.

An example histogram formatter 420 is included in the histogramgenerator 420 to format the color histogram determined by the imagesampler 405, the color quantizer 410 and the color counter 415 forsubsequent processing. For example, the histogram formatter 420 mayoutput a data array in which each element is indexed by a respectivepossible color combination and in which the element values correspond tothe counts of the different color combinations appearing in the sequenceof video frames sampled from a particular video and processed by thehistogram generator 400. In some examples, the histogram formatter 420may format the data array into a numeric value that may be used as asignature or, in other words, a color histogram signature, of the videocorresponding to the sequence of input images. For example, thehistogram formatter 420 may concatenate the bin values of the data arrayrepresenting the video's color histogram into a numeric value (e.g.,such as a binary value) forming the color histogram signature of thevideo.

A block diagram of an example implementation of the histogram comparator150 of FIG. 1 is illustrated in FIG. 5. The histogram comparator 150 ofFIG. 5 includes an example histogram interface 505 to obtain a colorhistogram of a test video (also referred to herein as the test colorhistogram) that is to be compared with a color histogram of a referencevideo (also referred to herein as the reference color histogram) alsoobtained via the example histogram interface 505. For example, thehistogram interface 505 may receive the test color histogram from thehistogram generator 145, and the histogram interface 505 may receive thereference color histogram from the histogram generator 120 and/or thereference histogram library 125. The histogram interface 505 can beimplemented by any type(s) of data interface(s), communication bus(ses),function(s), module(s), etc., capable of receiving the color histogramsand/or color histogram signatures from the histogram generators 120, 145and/or 400.

In the illustrated example, the histogram interface 505 enables thehistogram comparator 150 to determine multiple comparison metricsquantifying comparison of a reference video corresponding to a referencecolor histogram applied to the histogram interface 505 with a test videocorresponding to a test color histogram applied to the histograminterface 505. In particular, the histogram comparator 150 of theillustrated example determines a comparison metric based on differencesbetween bin values of a baseline color histogram corresponding to afirst video and adjusted bin values of a trial color histogramcorresponding to a second video. In the context of determiningcomparison metrics quantifying comparison of a reference video with atest video, the histogram comparator 150 enables different comparisonmetrics to be determined by assigning, for example, the reference colorhistogram to be the baseline color histogram and the test colorhistogram to be the trial color histogram to determine a firstcomparison metric, and then assigning the test color histogram to be thebaseline color histogram and the reference color histogram to be thetrial color histogram to determine a second comparison metric. In theillustrated example, the input color histogram (e.g., reference or testcolor histogram) assigned to be the trial color histogram is stored inan example trial histogram storage 510, and the input color histogram(e.g., reference or test color histogram) assigned to be the baselinecolor histogram is stored in an example baseline histogram storage 515.The trial histogram storage 510 and the baseline histogram storage 515can correspond to any type or combination of temporary and/or permanenttangible storage media, such as one or more of cache, volatile memory,flash memory, disk storage, etc., including but not limited to one ormore of the mass storage devices 1330 and/or volatile memory 1318 in theexample processing system 1300 of FIG. 13, which is described in greaterdetail below.

The example histogram comparator 150 of FIG. 5 also includes an examplebin adjuster 520 to determine adjusted bin values of the trial colorhistogram that are based on the bin values of the baseline colorhistogram and a scale factor. In the illustrated example, the binadjuster 520 determines the adjusted bin values of the trial colorhistogram by scaling bin values of the trial color histogram by a scalefactor (e.g., such as a scale factor of 2 or another value) to determinescaled bin values of the trial color histogram. As noted above, thescale factor can be a variable input parameter, a configurationparameter set during initialization, etc. Using the scaled bin values,the bin adjuster 520 compares the scaled bin values of the trial colorhistogram to the respective bin values of the baseline color histogramto determine the adjusted bin values of the trial color histogram.

For example, the bin adjuster 520 can determine an adjusted bin value ofthe trial color histogram to be the smaller of the respective scaled binvalue of the trial color histogram or the respective bin value of thebaseline color histogram. Mathematically, such an adjusted bin value fora particular color combination C in the test color histogram can bedetermined using Equation 1, which is:AdjustedHistogramTrial[C]=min{K×HistogramTrial[C],HistogramBaseline[C]}.  Equation 1In Equation 1, HistogramTrial[C] corresponds to the bin value for thecolor combination C in the trial color histogram, HistogramBaseline[C]corresponds to the bin value for the color combination C in the baselinecolor histogram, K is the scale factor used to scale the bin values ofthe trial color histogram to determine the scaled bin values, min{ } isa function that selects a minimum value from a set of input values, andAdjustedHistogramTrial[C] is the resulting adjusted bin value for thecolor combination C in the trial color histogram. An exampleimplementation of the bin adjuster 520 is illustrated in FIG. 6, whichis described in greater detail below.

The illustrated example histogram comparator 150 of FIG. 5 furtherincludes an example comparison metric determiner 525 to determine acomparison metric based on differences between bin values of thebaseline color histogram and the adjusted bin values of the trial colorhistogram. In some examples, the metric determiner 525 determines thecomparison metrics by determining the differences between the bin valuesof the baseline color histogram and the respective adjusted bin valuesof the trial color histogram for the same color combinations and summingthe differences to determine the comparison metric. In such examples,the difference between the bin value for the color combination C in thebaseline color histogram and the respective adjusted bin value for thecolor combination C in the trial color histogram can be representedmathematically as the quantity Difference[C] and determined usingEquation 2, which is:Difference[C]=HistogramBaseline[C]−min{K×HistogramTrial[C],HistogramBaseline[C]}.  Equation 2

Using Equation 2, the comparison metric can be representedmathematically as the quantity ComparisonMetric and determinedmathematically by summing the differences between the bin values of thebaseline color histogram and the respective adjusted bin values of thetrial color histogram in accordance with Equation 3, which is:ComparisonMetric=sum_(C){Difference[C]}=sum_(C){HistogramBaseline[C]−min{K×HistogramTrial[C],HistogramBaseline[C]}}.  Equation 3In Equation 3, sum_(C){ } denotes the sum over the set of possible colorcombinations {C} represented by the trial and baseline color histograms.An example implementation of the comparison metric determiner 525 isillustrated in FIG. 7, which is described in greater detail below.

In the illustrated example, the bin adjuster 520 and the comparisonmetric determiner 525 determine two comparison metrics quantifyingcomparison of the reference color histogram applied to the histograminterface 505 for a selected reference video with the test colorhistogram applied to the histogram interface 505 for a test video. Forthe first comparison metric, the reference color histogram for thereference video is assigned to be the baseline color histogram (whosebin values are not adjusted), and the test color histogram for the testvideo is assigned to be the trial color histogram (whose bin values areadjusted). For the second comparison metric, the test color histogramfor the test video is assigned to be the baseline color histogram (whosebin values are not adjusted), and the reference color histogram for thereference video is assigned to be the trial color histogram (whose binvalues are adjusted).

An example threshold comparator 530 is included in the example histogramcomparator 150 of FIG. 5 to compare the comparison metric(s) obtainedfrom the comparison metric determiner 525 to a threshold to determinewhether the particular reference video associated with input referencecolor histogram matches the test video associated with the input testcolor histogram. As noted above, the threshold can be a variable inputparameter, a configuration parameter set during initialization, etc. Inthe illustrated example, the threshold comparator 530 indicates that theparticular reference video is a match to the test video if either orboth of the first comparison metric (corresponding to the referencecolor histogram being the baseline color histogram and the test colorhistogram being the trial color histogram) and/or the second comparisonmetric (corresponding to the test color histogram being the baselinecolor histogram and the reference color histogram being the trial colorhistogram) is/are less than or equal to the threshold. Otherwise, ifboth comparison metrics are greater than the threshold, the thresholdcomparator 530 indicates that this particular reference video is not amatch to the test video.

A block diagram of an example implementation of the bin adjuster 520 ofFIG. 5 is illustrated in FIG. 6. The example bin adjuster 520 of FIG. 6includes an example bin scaler 605 and an example value selector 610. Inthe illustrated example, the bin scaler 605 determines the scaled binvalues of the trial color histogram by scaling the trial colorhistogram's bin values by the scale factor, as described above. Forexample, the bin scaler 605 can determine the scaled bin value for aparticular color combination C in the trial color histogram to beK×HistogramTrial[C], where HistogramTrial[C] corresponds to the binvalue for the color combination C in the trial color histogram, and K isthe scale factor used to scale the bin values of the trial colorhistogram to determine the scaled bin values.

The value selector 610 of the illustrated example determines theadjusted bin values of the trial color histogram to be the smaller ofthe scaled bin values of the trial color histogram as determined by thebin scaler 605 or the respective bin values of the baseline colorhistogram, as described above. For example, the value selector 610 canuse Equation 1, which is described above, to select the adjusted binvalue, AdjustedHistogramTrial[C], for the color combination C in thetrial color histogram to be the minimum of either the scaled bin value,K×HistogramTrial[C], for this color combination C in the trial colorhistogram or the respective bin value, HistogramBaseline[C], for thiscolor combination C in the baseline color histogram.

A block diagram of an example implementation of the comparison metricdeterminer 525 of FIG. 5 is illustrated in FIG. 7. The examplecomparison metric determiner 525 of FIG. 7 includes an example bindifference determiner 705 and an example difference summer 710. In theillustrated example, the bin difference determiner 705 determines thedifferences between bin values of the baseline color histogram andrespective adjusted bin values of the trial color histogram for the samecolor combinations. For example, the bin difference determiner 705 canuse Equation 2, which is described above, to determine, for each colorcombination C, the respective difference, Difference[C], between the binvalue for the color combination C in the baseline color histogram andthe respective adjusted bin value for the color combination C in thetrial color histogram.

The difference summer 710 of the illustrated example determines the sumof the differences obtained from the bin difference determiner 705. Forexample, the difference summer 710 can use Equation 3, which isdescribed above, to determine the sum, sum_(C){ }, of the differences,Difference[C], over the set of possible color combinations {C}. In theillustrated example, this sum forms the comparison metric thatquantifies the result of comparing the trial color histogram and thebaseline color histogram, as described above.

While example manners of implementing the video comparison system 100have been illustrated in FIGS. 1-7, one or more of the elements,processes and/or devices illustrated in FIGS. 1-7 may be combined,divided, re-arranged, omitted, eliminated and/or implemented in anyother way. Further, the example video frame samplers 110, 135 and/or200, the example histogram generators 120, 145 and/or 400, the exampletest video interface 130, the example histogram comparator 150, theexample results interface 155, the example image sampler 205, theexample sampling controller 210, the example image sampler 405, theexample color quantizer 410, the example color counter 415, the examplehistogram formatter 420, the example histogram interface 505, theexample bin adjuster 520, the example comparison metric determiner 525,the example threshold comparator 530, the example bin scaler 605, theexample value selector 610, the example bin difference determiner 705,the example difference summer 710 and/or, more generally, the examplevideo comparison system 100 of FIGS. 1-7 may be implemented by hardware,software, firmware and/or any combination of hardware, software and/orfirmware. Thus, for example, any of the example video frame samplers110, 135 and/or 200, the example histogram generators 120, 145 and/or400, the example test video interface 130, the example histogramcomparator 150, the example results interface 155, the example imagesampler 205, the example sampling controller 210, the example imagesampler 405, the example color quantizer 410, the example color counter415, the example histogram formatter 420, the example histograminterface 505, the example bin adjuster 520, the example comparisonmetric determiner 525, the example threshold comparator 530, the examplebin scaler 605, the example value selector 610, the example bindifference determiner 705, the example difference summer 710 and/or,more generally, the example video comparison system 100 could beimplemented by one or more circuit(s), programmable processor(s),application specific integrated circuit(s) (ASIC(s)), programmable logicdevice(s) (PLD(s)) and/or field programmable logic device(s) (FPLD(s)),etc. When any of the apparatus or system claims of this patent are readto cover a purely software and/or firmware implementation, at least oneof the example video comparison system 100, the example video framesamplers 110, 135 and/or 200, the example histogram generators 120, 145and/or 400, the example test video interface 130, the example histogramcomparator 150, the example results interface 155, the example imagesampler 205, the example sampling controller 210, the example imagesampler 405, the example color quantizer 410, the example color counter415, the example histogram formatter 420, the example histograminterface 505, the example bin adjuster 520, the example comparisonmetric determiner 525, the example threshold comparator 530, the examplebin scaler 605, the example value selector 610, the example bindifference determiner 705 and/or the example difference summer 710 arehereby expressly defined to include a tangible computer readable mediumsuch as a memory, digital versatile disk (DVD), compact disk (CD),Blu-ray disc™, etc., storing such software and/or firmware. Furtherstill, the example video comparison system 100 as illustrated in FIGS.1-7 may include one or more elements, processes and/or devices inaddition to, or instead of, those illustrated in FIGS. 1-7, and/or mayinclude more than one of any or all of the illustrated elements,processes and devices.

Flowcharts representative of example machine readable instructions forimplementing the example video comparison system 100, the example videoframe samplers 110, 135 and/or 200, the example histogram generators120, 145 and/or 400, the example test interface 130, the examplehistogram comparator 150, the example results interface 155, the exampleimage sampler 205, the example sampling controller 210, the exampleimage sampler 405, the example color quantizer 410, the example colorcounter 415, the example histogram formatter 420, the example histograminterface 505, the example bin adjuster 520, the example comparisonmetric determiner 525, the example threshold comparator 530, the examplebin scaler 605, the example value selector 610, the example bindifference determiner 705 and/or the example difference summer 710 areshown in FIGS. 8-12. In these examples, the machine readableinstructions represented by each flowchart may comprise one or moreprograms for execution by a processor, such as the processor 1312 shownin the example processing system 1300 discussed below in connection withFIG. 13. The one or more programs, or portion(s) thereof, may beembodied in software stored on a tangible computer readable storagemedium such as a CD-ROM, a floppy disk, a hard drive, a digitalversatile disk (DVD), a Blu-ray disc™, or a memory associated with theprocessor 1312, but the entire program or programs and/or portionsthereof could alternatively be executed by a device other than theprocessor 1312 (e.g., such as a controller and/or any other suitabledevice) and/or embodied in firmware or dedicated hardware (e.g.,implemented by an ASIC, a PLD, an FPLD, discrete logic, etc.). Also, oneor more of the machine readable instructions represented by theflowchart of FIGS. 8-12 may be implemented manually. Further, althoughthe example machine readable instructions are described with referenceto the flowcharts illustrated in FIGS. 8-12, many other methods ofimplementing the example video comparison system 100, the example videoframe samplers 110, 135 and/or 200, the example histogram generators120, 145 and/or 400, the example test interface 130, the examplehistogram comparator 150, the example results interface 155, the exampleimage sampler 205, the example sampling controller 210, the exampleimage sampler 405, the example color quantizer 410, the example colorcounter 415, the example histogram formatter 420, the example histograminterface 505, the example bin adjuster 520, the example comparisonmetric determiner 525, the example threshold comparator 530, the examplebin scaler 605, the example value selector 610, the example bindifference determiner 705 and/or the example difference summer 710 mayalternatively be used. For example, with reference to the flowchartsillustrated in FIGS. 8-12, the order of execution of the blocks may bechanged, and/or some of the blocks described may be changed, eliminated,combined and/or subdivided into multiple blocks.

As mentioned above, the example processes of FIGS. 8-12 may beimplemented using coded instructions (e.g., computer readableinstructions) stored on a tangible computer readable medium such as ahard disk drive, a flash memory, a read-only memory (ROM), a CD, a DVD,a cache, a random-access memory (RAM) and/or any other storage media inwhich information is stored for any duration (e.g., for extended timeperiods, permanently, brief instances, for temporarily buffering, and/orfor caching of the information). The tangible computer readable mediumcan be local to and/or remote from the processor(s), device(s),apparatus, etc., that is/are to execute the coded instructions. As usedherein, the term tangible computer readable medium is expressly definedto include any type of computer readable storage and to excludepropagating signals. Additionally or alternatively, the exampleprocesses of FIGS. 8-12 may be implemented using coded instructions(e.g., computer readable instructions) stored on a non-transitorycomputer readable medium, such as a flash memory, a ROM, a CD, a DVD, acache, a random-access memory (RAM) and/or any other storage media inwhich information is stored for any duration (e.g., for extended timeperiods, permanently, brief instances, for temporarily buffering, and/orfor caching of the information). As used herein, the term non-transitorycomputer readable medium is expressly defined to include any type ofcomputer readable medium and to exclude propagating signals. Also, asused herein, the terms “computer readable” and “machine readable” areconsidered equivalent unless indicated otherwise. Furthermore, as usedherein, when the phrase “at least” is used as the transition term in apreamble of a claim, it is open-ended in the same manner as the term“comprising” is open ended. Thus, a claim using “at least” as thetransition term in its preamble may include elements in addition tothose expressly recited in the claim.

Example machine readable instructions 800 that may be executed toimplement the example video comparison system 100 of FIG. 1 arerepresented by the flowchart shown in FIG. 8. The example machinereadable instructions 800 may be executed, for example, when a testvideo is to be compared with one or more reference videos. Withreference to the preceding figures, the machine readable instructions800 of FIG. 8 begin execution at block 805 at which the test videointerface 130 of the video comparison system 100 obtains, as describedabove, a test (e.g., input) video for comparison with a reference videostored in the reference video library 105. At block 810, the video framesampler 135 of the video comparison system 100 samples or otherwiseobtains a sequence of test video frames (and/or sampledpixel(s)/subregion(s) of the test video frames) from the test video, asdescribed above. At block 815, the histogram generator 145 of the videocomparison system 100 determines a test color histogram, as describedabove, for the sequence of test video frames obtained at block 810 forthe test video obtained at block 805. In some examples, at block 815 thehistogram generator 145 can process the sequence of test video frames(and/or sampled pixels(s)/subregion(s) of the test video frames)individually to accumulate a test color histogram for the test video,whereas in other examples, the histogram generator 145 can process acomposite test image, as described above. Example machine readableinstructions that may be used to implement the processing at block 815are illustrated in FIG. 9, which is described in greater detail below.

At block 820 the video comparison system 100 accesses the referencehistogram library 125 of the video comparison system 100 to obtain areference color histogram for a reference video in the reference videolibrary 105 to be compared with the test video. As described above, thehistogram generator 120 of the video comparison system 100 can be usedto generate a reference color histogram for the reference video usingprocessing similar to the processing (e.g., such as the processing atblock 815) performed to generate the test color histogram for the testvideo.

At block 825, the histogram comparator 150 of the video comparisonsystem 100 determines adjusted bin values of the test color histogramgenerated at block 815 for the test video for use in determining a firstcomparison metric quantifying comparison of the test video with thereference video. For example, at block 825, the bin adjuster 520 of thehistogram comparator 150 uses the bin values of the reference colorhistogram obtained at block 820 and a scale factor, as described above,to determine the adjusted bin values of the test color histogram.Example machine readable instructions that may be used to implement theprocessing at block 825 are illustrated in FIG. 10, which is describedin greater detail below.

At block 830, the histogram comparator 150 determines, based on the binvalues of the reference color histogram obtained at block 820 and theadjusted bin values of the test color histogram determined at block 825,a first comparison metric that quantifies the results of comparing thereference video with the test video. For example, at block 830, thecomparison metric determiner 525 of the histogram comparator 150 candetermine the first comparison metric by summing the differences betweenbin values of the reference color histogram and respective adjusted binvalues of the test color histogram, as described above. Example machinereadable instructions that may be used to implement the processing atblock 830 are illustrated in FIG. 11, which is described in greaterdetail below.

At block 835, the histogram comparator 150 of the video comparisonsystem 100 determines adjusted bin values of the reference colorhistogram obtained at block 820 for the reference video for use indetermining a second comparison metric quantifying comparison of thetest video with the reference video. For example, at block 835, the binadjuster 520 of the histogram comparator 150 uses the bin values of thetest color histogram generated at block 815 for the test video and ascale factor, as described above, to determine the adjusted bin valuesof the reference color histogram. Example machine readable instructionsthat may be used to implement the processing at block 835 areillustrated in FIG. 10, which is described in greater detail below.

At block 840, the histogram comparator 150 determines, based on the binvalues of the test color histogram determined at block 815 and theadjusted bin values of the reference color histogram determined at block835, a second comparison metric that quantifies the results of comparingthe reference video with the test video. For example, at block 840, thecomparison metric determiner 525 of the histogram comparator 150 candetermine the second comparison metric by summing the differencesbetween bin values of the test color histogram and respective adjustedbin values of the reference color histogram, as described above. Examplemachine readable instructions that may be used to implement theprocessing at block 840 are illustrated in FIG. 11, which is describedin greater detail below.

At block 845, the threshold comparator 530 of the histogram comparator150 compares the first and second comparison metrics quantifyingcomparison of the test video with the reference video to a threshold, asdescribed above. In the illustrated example, if at least one of thefirst comparison metric and/or the second comparison is less than orequal to the threshold (or otherwise meets the threshold) at block 845,then at block 850 the histogram comparator 150 identifies the referencevideo as being a match of the test video. However, if both the first andsecond comparison metrics are greater than the threshold (or otherwisedo not meet the threshold) at block 845, then at block 855 the histogramcomparator 150 indicates that the reference video does not match thetest video. Execution of the example machine readable instructions 800then ends.

Example machine readable instructions 815 that may be used to implementone or more of the histogram generators 120, 145 and/or 400, and/or toperform the processing at block 815 of FIG. 8, are illustrated in FIG.9. For brevity, execution of the machine readable instructions 815 ofFIG. 9 is described from the perspective of implementation by thehistogram generator 400. However, the machine readable instructions 815of FIG. 9 could additionally or alternatively be executed by thehistogram generators 120 and/or 145.

With reference to the preceding figures, execution of the machinereadable instructions 815 of FIG. 9 begins at block 905 at which theimage sampler 405 of the histogram generator 400 samples, as describedabove, pixels of an input sequence of video frames of a video or,alternatively, a composite image formed from the sequence of videoframes, to determine a set of pixels of the video for which a colorhistogram is to be determined. At block 910, the color quantizer 410 ofthe histogram generator 400 quantizes the color values (e.g., threecolor values, such as red, blue and green) of the sampled pixels intorespective sets of color levels, as described above, to yield a totalnumber of possible color combinations and, thus, a total number of colorbins represented by the color histogram. At block 915, the color counter415 of the histogram generator 400 counts the numbers of times eachpossible quantized color combination appears in the sampled set ofpixels to determine the bin values of the color bins of the colorhistogram. At block 920, the histogram formatter 420 of the histogramgenerator 400 formats the bin values of the color bins into a colorhistogram data representation, such as a color histogram signature, forthe input video, which may be stored and/or used in subsequentprocessing. Execution of the example machine readable instructions 815then ends.

Example machine readable instructions 1000 that may be used to implementthe bin adjuster 520 of the histogram comparator 150, and/or to performthe processing at blocks 825 and/or 835 of FIG. 8, are illustrated inFIG. 10. With reference to the preceding figures, execution of themachine readable instructions 1000 of FIG. 10 begins at block 1005 atwhich the bin adjuster 520 obtains the scale factor described above. Atblock 1010, the bin adjuster 520 scales the bin values of a trial colorhistogram by the scale factor obtained at block 1005 to obtain scaledbin values of the trial color histogram, as described above. Forexample, to determine the first comparison metric described above thatquantifies comparison of the test video and the reference video, thehistogram interface 505 of the histogram comparator 150 assigns the testcolor histogram representative of the test video to be the trial colorhistogram processed at block 1010. As another example, to determine thesecond comparison metric described above that quantifies comparison ofthe test video and the reference video, the histogram interface 505assigns the reference color histogram representative of the referencevideo to be the trial color histogram processed at block 1010.

At block 1015, the bin adjuster 520 begins processing to adjust each binvalue of the trial color histogram. For example, at block 1020, the binadjuster 520 determines the adjusted bin value for a particular colorbin to be the smaller, or minimum, of the scaled bin value for thiscolor bin or the bin value of a baseline color histogram, as describedabove. For example, to determine the first comparison metric describedabove that quantifies comparison of the test video and the referencevideo, the histogram interface 505 assigns the reference color histogramrepresentative of the reference video to be the baseline color histogramused in the processing at block 1020. As another example, to determinethe second comparison metric described above that quantifies comparisonof the test video and the reference video, the histogram interface 505assigns the test color histogram representative of the test video to bethe baseline color histogram used in the processing at block 1020. Afterthe bin values of the trial color histogram have been adjusted (block1025), at block 1030 the bin adjuster 520 outputs the adjusted binvalues determined for the trial color histogram. For example, theadjusted trial color histogram output at block 1030 corresponds to theadjusted test color histogram when determining the first comparisonmetric described above, whereas the adjusted trial color histogramoutput at block 1030 corresponds to the adjusted reference colorhistogram when determining the second comparison metric described above.Execution of the example machine readable instructions 1000 then ends.

Example machine readable instructions 1100 that may be used to implementthe comparison metric determiner 525 of the histogram comparator 150,and/or to perform the processing at blocks 830 and/or 840 of FIG. 8, areillustrated in FIG. 11. With reference to the preceding figures,execution of the machine readable instructions 1100 of FIG. 11 begins atblock 1105 at which the comparison metric determiner 525 obtains abaseline color histogram for use in determining a comparison metricquantifying comparison of the reference video with the test video. Forexample, to determine the first comparison metric described above thatquantifies comparison of the test video and the reference video, thehistogram interface 505 assigns the reference color histogramrepresentative of the reference video to be the baseline color histogramobtained at block 1105. As another example, to determine the secondcomparison metric described above that quantifies comparison of the testvideo and the reference video, the histogram interface 505 assigns thetest color histogram representative of the test video to be the baselinecolor histogram obtained at block 1105. At block 1110, the comparisonmetric determiner 525 obtains the adjusted trial color histogram havingadjusted bin values as determined by, for example, the bin adjuster 520,the example machine readable instructions 825, etc. For example, theadjusted trial color histogram obtained at block 1110 corresponds to theadjusted test color histogram when determining the first comparisonmetric described above, whereas the adjusted trial color histogramobtained at block 1110 corresponds to the adjusted reference colorhistogram when determining the second comparison metric described above.

At block 1115, the comparison metric determiner 525 begins determiningdifferences between bin values of the baseline color histogram andrespective adjusted bin values of the adjusted trial color histogram.For example, at block 1120, the comparison metric determiner 525determines, for each color bin, a difference between the bin value ofthe baseline color histogram and the adjusted bin value of the trialcolor histogram for the particular color bin. After the differences forall color bins have been determined (block 1125), at block 1130 thecomparison metric determiner 525 sums the difference values determinedfor each color bin to determine a comparison metric (e.g., the firstcomparison metric or the second comparison metric described above)quantifying comparison of the reference video with the test video.Execution of the example machine readable instructions 1100 then ends.

Example machine readable instructions 1200 that may be executed todetermine the reference color histograms stored in the referencehistogram library 125 of the example video comparison system 100 and/orobtained at block 820 of example machine readable instructions 800 arerepresented by the flowchart shown in FIG. 12. With reference to thepreceding figures, execution of the example machine readableinstructions 1200 of FIG. 12 begins at block 1205 at which the videoframe sampler 110 obtains the reference video(s) from the referencevideo library 105 for which reference color histogram(s) is(are) to bedetermined. At block 1210, video frame sampler 110 samples or otherwiseobtains sequence(s) of video frames (and/or sampledpixel(s)/subregion(s) of the reference video frames) from the referencevideo(s), as described above. In some examples, the video frame sampler110 also determines composite reference image(s) by tiling thesequence(s) of reference video frames (and/or sampledpixel(s)/subregion(s) of the reference video frames) at block 1210. Atblock 1215, the histogram generator 120 determines the reference colorhistogram(s) for the reference videos(s) using the sequence(s) ofreference video frames and/or composite reference image(s) obtained atblock 1210, as described above. For example, the histogram generator 120can execute the example machine readable instructions 815 illustrated inFIG. 9 to determine the reference color histogram(s) at block 1215. Atblock 1220, the histogram generator 120 stores the generated referencecolor histogram(s) in the reference histogram library 125. Execution ofthe example machine readable instructions 1200 then ends.

FIG. 13 is a block diagram of an example processing system 1300 capableof executing the instructions of FIGS. 8-12 to implement the examplevideo comparison system 100, the example video frame samplers 110, 135and/or 200, the example histogram generators 120, 145 and/or 400, theexample test video interface 130, the example histogram comparator 150,the example results interface 155, the example image sampler 205, theexample sampling controller 210, the example image sampler 405, theexample color quantizer 410, the example color counter 415, the examplehistogram formatter 420, the example histogram interface 505, theexample bin adjuster 520, the example comparison metric determiner 525,the example threshold comparator 530, the example bin scaler 605, theexample value selector 610, the example bin difference determiner 705and/or the example difference summer 710 of FIGS. 1-7. The processingsystem 1300 can be, for example, a server, a personal computer, a mobilephone (e.g., a smartphone, a cell phone, etc.), a personal digitalassistant (PDA), an Internet appliance, a DVD player, a CD player, adigital video recorder, a Blu-ray player, a gaming console, a personalvideo recorder, a set top box, a digital camera, or any other type ofcomputing device.

The system 1300 of the instant example includes a processor 1312. Forexample, the processor 1312 can be implemented by one or moremicroprocessors and/or controllers from any desired family ormanufacturer. The processor 1312 includes a local memory 1314, andexecutes coded instructions 1316 present in the local memory 1314 and/orin another memory device.

The processor 1312 is in communication with a main memory including avolatile memory 1318 and a non-volatile memory 1320 via a bus 1322. Thevolatile memory 1318 may be implemented by Static Random Access Memory(SRAM), Synchronous Dynamic Random Access Memory (SDRAM), Dynamic RandomAccess Memory (DRAM), RAMBUS Dynamic Random Access Memory (RDRAM) and/orany other type of random access memory device. The non-volatile memory1320 may be implemented by flash memory and/or any other desired type ofmemory device. Access to the main memory, including the memories 1318and 1320, is controlled by a memory controller.

The processing system 1300 also includes an interface circuit 1324. Theinterface circuit 1324 may be implemented by any type of interfacestandard, such as an Ethernet interface, a universal serial bus (USB),and/or a PCI express interface.

One or more input devices 1326 are connected to the interface circuit1324. The input device(s) 1326 permit a user to enter data and commandsinto the processor 1312. The input device(s) can be implemented by, forexample, a keyboard, a mouse, a touchscreen, a track-pad, a trackball, atrackbar (such as an isopoint), a voice recognition system, and/or anyother human-machine interface.

One or more output devices 1328 are also connected to the interfacecircuit 1324. The output devices 1328 can be implemented, for example,by display devices (e.g., a liquid crystal display, a cathode ray tubedisplay (CRT)), by a printer and/or by speakers. The interface circuit1324, thus, typically includes a graphics driver card.

The interface circuit 1324 also includes a communication device such asa modem or network interface card to facilitate exchange of data withexternal computers via a network (e.g., an Ethernet connection, adigital subscriber line (DSL), a telephone line, coaxial cable, acellular telephone system, etc.).

The processing system 1300 also includes one or more mass storagedevices 1330 for storing machine readable instructions and data.Examples of such mass storage devices 1330 include floppy disk drives,hard drive disks, compact disk drives and digital versatile disk (DVD)drives. In some examples, the mass storage device 1330 may implement thereference video library 105, the composite reference image storage 115,the reference histogram library 125, the composite test image storage140, the trial histogram storage 510 and/or the baseline histogramstorage 515. Additionally or alternatively, in some examples thevolatile memory 1318 may implement the reference video library 105, thecomposite reference image storage 115, the reference histogram library125, the composite test image storage 140, the trial histogram storage510 and/or the baseline histogram storage 515.

Coded instructions 1332 corresponding to the instructions of FIGS. 8-12may be stored in the mass storage device 1330, in the volatile memory1318, in the non-volatile memory 1320, in the local memory 1314 and/oron a removable storage medium, such as a CD or DVD 1336.

As an alternative to implementing the methods and/or apparatus describedherein in a system such as the processing system of FIG. 13, the methodsand or apparatus described herein may be embedded in a structure such asa processor and/or an ASIC (application specific integrated circuit).

Finally, although certain example methods, apparatus and articles ofmanufacture have been described herein, the scope of coverage of thispatent is not limited thereto. On the contrary, this patent covers allmethods, apparatus and articles of manufacture fairly falling within thescope of the appended claims either literally or under the doctrine ofequivalents.

What is claimed is:
 1. A method to compare video sequences, the methodcomprising: determining a color histogram corresponding to an inputvideo sequence based on color values of pixels sampled from a pluralityof video frames of the input video sequence; tiling video frames of afirst reference video sequence to determine a composite image;determining a first reference color histogram corresponding to the firstreference video sequence based on color values of pixels in thecomposite image; adjusting the color histogram corresponding to theinput video sequence based on the first reference color histogramcorresponding to the first reference video sequence to determine anadjusted color histogram corresponding to the input video sequence; andcomparing the adjusted color histogram and the first reference colorhistogram to determine whether the first reference video sequencematches the input video sequence.
 2. A method as defined in claim 1,wherein determining the color histogram corresponding to the input videosequence includes: sampling a set of pixels from the plurality of videoframes of the input video sequence; determining respective colorcombinations for respective ones of the set of pixels, a first colorcombination for a first one of the set of pixels being determined bycombining a first color value for the first one of the set of pixels anda second color value for a neighboring pixel of the first one of the setof pixels; and counting respective occurrences of different ones of thecolor combinations to determine the color histogram corresponding to theinput video sequence.
 3. A method as defined in claim 2, furtherincluding: capturing the input video sequence using a camera operatingat a first frame rate; sampling the input video sequence at a secondframe rate lower than the first frame rate to obtain the plurality ofvideo frames of the input video sequence; and displaying a resultindicating whether the first reference video sequence matches the inputvideo sequence.
 4. A method as defined in claim 1, further including:determining a first comparison value by comparing the adjusted colorhistogram and the first reference color histogram; adjusting the firstreference color histogram based on the color histogram corresponding tothe input video sequence to determine a first adjusted reference colorhistogram; determining a second comparison value by comparing the firstadjusted reference color histogram and the color histogram correspondingto the input video sequence; and determining that the first referencevideo sequence matches the input video sequence when at least one of thefirst comparison value or the second comparison value satisfies athreshold.
 5. A method as defined in claim 1, wherein adjusting thecolor histogram corresponding to the input video sequence based on thefirst reference color histogram includes: multiplying a value of a firstbin of the color histogram corresponding to the input video sequence bya scale factor to determine a scaled bin value; and determining anadjusted value of a corresponding first bin of the adjusted colorhistogram to be a smaller of the scaled bin value and a value of acorresponding first bin of the reference color histogram.
 6. A method asdefined in claim 5, wherein the scale factor is adjustable.
 7. Atangible computer readable medium comprising computer readableinstructions which, when executed, cause a processor to at least:determine a color histogram corresponding to an input video sequencebased on color values of pixels sampled from a plurality of video framesof the input video sequence; tile video frames of a first referencevideo sequence to determine a composite image; determine a firstreference color histogram corresponding to the first reference videosequence based on color values of pixels in the composite image; adjustthe color histogram corresponding to the input video sequence based onthe first reference color histogram corresponding to the first referencevideo sequence to determine an adjusted color histogram corresponding tothe input video sequence; and compare the adjusted color histogram andthe first reference color histogram to determine whether the firstreference video sequence matches the input video sequence.
 8. A tangiblecomputer readable medium as defined in claim 7, wherein to determine thecolor histogram corresponding to the input video sequence, theinstructions, when executed, cause the processor to: sample a set ofpixels from the plurality of video frames of the input video sequence;determine respective color combinations for respective ones of the setof pixels, a first color combination for a first one of the set ofpixels being determined by combining a first color value for the firstone of the set of pixels and a second color value for a neighboringpixel of the first one of the set of pixels; and count respectiveoccurrences of different ones of the color combinations to determine thecolor histogram corresponding to the input video sequence.
 9. A tangiblecomputer readable medium as defined in claim 8, wherein theinstructions, when executed, further cause the processor to: capture theinput video sequence using a camera operating at a first frame rate;sample the input video sequence at a second frame rate lower than thefirst frame rate to obtain the plurality of video frames of the inputvideo sequence; and display a result indicating whether the firstreference video sequence matches the input video sequence.
 10. Atangible computer readable medium as defined in claim 7, wherein theinstructions, when executed, further cause the processor to: determine afirst comparison value by comparing the adjusted color histogram and thefirst reference color histogram; adjust the first reference colorhistogram based on the color histogram corresponding to the input videosequence to determine a first adjusted reference color histogram;determine a second comparison value by comparing the first adjustedreference color histogram and the color histogram corresponding to theinput video sequence; and determine that the first reference videosequence matches the input video sequence when at least one of the firstcomparison value or the second comparison value satisfies a threshold.11. A tangible computer readable medium as defined in claim 7, whereinto adjust the color histogram corresponding to the input video sequencebased on the first reference color histogram, the instructions, whenexecuted, further cause the processor to: multiply a value of a firstbin of the color histogram corresponding to the input video sequence bya scale factor to determine a scaled bin value; and determine anadjusted value of a corresponding first bin of the adjusted colorhistogram to be a smaller of the scaled bin value and a value of acorresponding first bin of the reference color histogram.
 12. A tangiblecomputer readable medium as defined in claim 11, wherein the scalefactor is adjustable.
 13. An apparatus to compare video sequences, theapparatus comprising: a histogram generator to determine a colorhistogram corresponding to an input video sequence based on color valuesof pixels sampled from a plurality of video frames of the input videosequence; and a histogram comparator to: adjust the color histogramcorresponding to the input video sequence based on a first referencecolor histogram corresponding to a first reference video sequence todetermine an adjusted color histogram corresponding to the input videosequence; and compare the adjusted color histogram and the firstreference color histogram to determine whether the first reference videosequence matches the input video sequence; wherein the histogramcomparator includes a bin adjuster to: multiply a value of a first binof the color histogram corresponding to the input video sequence by ascale factor to determine a scaled bin value; and determine an adjustedvalue of a corresponding first bin of the adjusted color histogram to bea smaller of the scaled bin value and a value of a corresponding firstbin of the reference color histogram.
 14. An apparatus as defined inclaim 13, wherein the a histogram generator includes: an image samplerto sample a set of pixels from the plurality of video frames of theinput video sequence; a color quantizer to determine respective colorcombinations for respective ones of the set of pixels, a first colorcombination for a first one of the set of pixels being determined bycombining a first color value for the first one of the set of pixels anda second color value for a neighboring pixel of the first one of the setof pixels; and a color counter to count respective occurrences ofdifferent ones of the color combinations to determine the colorhistogram corresponding to the input video sequence.
 15. An apparatus asdefined in claim 14, further including: a video interface to capture theinput video sequence using a camera operating at a first frame rate; avideo frame sampler to sample the input video sequence at a second framerate lower than the first frame rate to obtain the plurality of videoframes of the input video sequence; and a results interface to display aresult indicating whether the first reference video sequence matches theinput video sequence.
 16. An apparatus as defined in claim 13, whereinthe histogram comparator includes: a bin adjuster to: determine theadjusted color histogram; and adjust the first reference color histogrambased on the color histogram corresponding to the input video sequenceto determine a first adjusted reference color histogram; a comparisonmetric determiner to: determine a first comparison value by comparingthe adjusted color histogram and the first reference color histogram;and determine a second comparison value by comparing the first adjustedreference color histogram and the color histogram corresponding to theinput video sequence; and a threshold comparator to determine that thefirst reference video sequence matches the input video sequence when atleast one of the first comparison value or the second comparison valuesatisfies a threshold.
 17. An apparatus as defined in claim 13, whereinthe scale factor is adjustable.